US3786247A

US3786247A - Optical illumination system

Info

Publication number: US3786247A
Application number: US00780124A
Authority: US
Inventors: R Eilert; J Klemenz
Original assignee: Chicago Aerial Industries Inc
Current assignee: Recon Optical Inc
Priority date: 1968-11-29
Filing date: 1968-11-29
Publication date: 1974-01-15
Anticipated expiration: 1991-01-15

Abstract

An optical illumination system for aerial electronic flash photography which employs one or more illumination modules each of which includes a cylindrical light source and a unique troughlike reflector configuration for providing weighted distribution of emitted light to compensate for attenuation factors such as slant range and lens optical fall-off.

Description

[ Jan. 15, 1974 United States Patent [191 Eilert et al.

FOREIGN PATENTS OR APPLICATIONS ml Ta t n e r. n mew lar- EBB 00899 6666 9 999 llll UWWU .l 32 9 976 3 096 69400 33 3333 OPTICAL ILLUMINATION SYSTEM [75] Inventors: Richard L. Eilert, Palatine; John J. Klemenz, Mount Prospect, both of III.

3343 O O wwww 4 4 2 2 TmJmU 88 t! m mm m: err. GGG 2267 5344 9999 HUM 9 82 26. 2 303 4 9595 4679 8355 C n 1 m .mP U Sn 0 dt n I mm m a U f M o 9 e w C :lu.v h 0 CV N e n .wr d s m A F .l 3 2 7 2 .l. .l.

Great Britain....................r.

21 Appl. No.: 780,124

Primary ExaminerRobert P. Greinei' C 11 3 nmk Our .JHd a m e1, 1 y mc m m 3 ;1 e r m OOC T w Cm h h Wow .B mm m C .m m m; ma w lr mo n w 7 Sf aa UAfln 3 .M9 0 11531 WWIOA. 4 4b ,M3 N GH 0/ 0 40 4 24 2/ ,2 m 3 ".m L MHZ I." 0 "n 4 u 2 n .c u "r n u u& L cm C I 3 h U .mF l I] 2 I00 5 55 I ll References Cited UNITED STATES PATENTS light source and a unique trough-like reflector configuration for providing weighted distribution of emitted light to compensate for attenuation factors such as slant range and lens optical fall-off.

7 Claims, 17 Drawing Figures O "n 4 u 2 mmM m m m i an mm ayk oan DNA 166 456 99.9 111 42 975 728 049 432 223 PAIENIEU 51786.24?

SHEEI 1 BF 5 Inventors Richard LEilerT John J. Klemenz Attorneys PATENIEDJAN I 5

I574 sum

2 or 5 Zmww Fin 6 96 MT m,

Emh

m .l A

M F J PATENTEUJANISIW 5.186.241

SHEEI [If 5 FICHO Direcrion of Flight Relorive Ampli'fude of Ground Ir'rodionce o IGIO O O O F 5.00 7.|0 I059 O O O O O O O o o o 0 2.77 L77 1.66 2.06 3.03 4.77 7.57

O O O Richard L.Eilerr John J. Klemenz Attorneys PATENTEUJAN I 51974 SHEET 5 BF 5 Inventors FIG.

5 l .r 0 6 5 2 2 5 6 O .r .l 4 2 2 5 5 w .l 2 2 me. W. 6 23 5 rs II (C 3 H 3 .r 5 I O 5 5 v 5 2 5 5 Q2 M Q N 2 H2 l 2 C l: 5. v/ I H ,H 52

Richard L.Ei|err John J. Klemenz By 2 W frorneys FIG.

OPTICAL ILLUMINATION SYSTEM This invention relates generally to an optical illumination system and, more particularly, to an optical illumination system for aerial electronic flash photography.

Equipment which provides a .so-called electronic photography, continuing efforts are being made to overcome the problems in the use of electronic flash equipment in this field. Thus far, these efforts have been largely directed toward improving the flash tubes and developing lighter weight power supplies. However, up to this time very little has been accomplished with regard to the development of more efficient techniques for distributing the emitted illumination with the exception of the Illumination Optical System disclosed by Walter L. Colterjohn in U.S. Pat. No. 3,251,984 and the Optical Illumination System disclosed by Thomas L. Thompson and Theodore J. Schulze in U.S. Pat. No. 3,375,36l. Although the Colterjohn and Thompson et al patents show significant accomplishment in terms of efficiency and uniformity of distribution, there has remained a considerable need for an optical illumination system which has the capability for providing an efficient, well defined illumination intensity distribution which will compensate in a given application for variations in the slant range from the illumination source and for the effects of lens fall-off and which has the capability of ready adaptability to formats of differing illumination intensity distribution requirements, configuration, and size. Moreover, the attainment of these capabilities has been most difficult because of the severe limitations of space availability for the optical illumination system on aircraft coupled with the use of light sources of increasing greater energy output and the concomitant problem of cooling, in a limited space, equipment which provides short duration but extremely large, repetitive energy output.

Therefore, it is a general object of this invention to provide a new and improved optical illumination system for use in aerial flash photography.

It is another general object of this invention to provide an improved optical illumination system which makes .more efficient use of the emitted illumination then previous systems.

It is a primay object of this invention to provide an optical illumination system which distributes illumination intensity with compensation for variations in the slant ranges from the illumination source and for lens optical fall-off.

Another primary object of this invention is to provide an optical illumination system which is readily adapt able to differing format configurations and size.

It is another object of this invention to provide an optical illumination system for aircraft which is adaptable to the space-availability limitations on aircraft.

Still another object of this invention is to prolong the life of the equipment by animproved system of heat dissipation.

These and other objects of the present invention are achieved by the employment of a novel illumination reflector system. Briefly, the invention is basedon the discovery that a weighted reflective surface which is uniquely capable of efficiently distributing emitted illumination in a manner which will compensate for variations in slant range, lens fall-off, and other inequalities can be generated about a cylindrical light source in accordance with the recognition that the light emitted from a cylindrical light source is incident upon a point on a parallel reflective surface in the form of a set of convergent rays having a convergence angle which is dependent upon the radius of the cylindrical light source and distance of the point of incidence from the geometric axis of the lightsource and that the emitted light is reflected from the point of incidence in the form of a set of divergent rays having a divergence angle which is dependent upon the convergence angle of the set of incident light rays and a direction which is dependent upon the slope of the reflective surface at the point of incidence. In particular, the present invention involves the employment of a reflective surface which is generated to extend through a series of points each located at a distance from the geometric axis of the cylindrical light source and at a slope such that (l) at each of the points in the series, the tangentially-emitted incident ray nearer the desired aperture of the reflector is reflected at the same predetermined angle with respect to the plane defined by the geometric axis of the light source and the center line of the desired illumination beam so as to fall upon the opposite, outermost edge of the desired illumination format and (2) the divergence angle of the set of reflected rays is gradually reduced at each of the points in the series so as to diminish from a predetermined maximum angle at the rearmost point on the surface to a predetermined minimum angle at the fo'rwardmost point on the reflective surface. Before proceeding further with a description of the invention, it may be well to review at this point certain background considerations.

The camera normally employed in aerial photography has a square or rectangular format area. The optical illumination system, therefore, should be capable of illuminating a ground format which is coincident with the area imaged upon the camera format. Because sufficient light output must be provided to insure adequate film exposure at the operating altitude (taking into account photographic parameters such as lens relative aperture, film sensitivity, spectral considerations, and scene reflectance characteristics), the ground format must be efficiently illuminated with a minimum of spill of illumination into the region outside of the ground format. Moreover, the illumination beam should have an intensity distribution such that proper compensation is obtained for variations in slant range from the illuminator source to points on the ground form at and for the effects of lens fall-off. Basically, these are the accomplishments of the inventive illumination system.

In a typical system embodiment of the invention, one or more illumination modules have reflective surfaces generated in the manner previously noted are oriented parallel to the direction of flight, and one or more such reflector units are oriented perpendicular to the direction of flight. The reflector units oriented parallel to the flight path provide format illumination weighted to compensate for attenuation due to slant range and lens fall-off in the port and starboard directions. The reflector units oriented perpendicular to the flight path provide format illumination weighted to compensate for attenuation due to slant range and lens fall-off in the fore and aft directions. The system is readily adaptable to formats of differing illumination intensity distribution requirements, configurations, and size, and will adapt to limitations on space availability on aircraft and accommodate the use of cylindrical light sources of increasing greater energy output. It has been found that the system can be effectively cooled by mounting the cylindrical light sources within quartz tubes and providing a manifold system which passes ram intake air through the quartz tubes.

In addition to increased format illumination distribution efficiency, significant improvement in system illumination output efficiency has been achieved with the reflectors of the present invention, largely due to the reflectors increased collection efficiency in a smaller physical size and because the reflector utilizes radiation directly from the light source. In the prior parabolic aerial illumination system reflector units, the sides of the lamps away from the main parabolic reflector were covered by small reflectors which reflected half of the lamp output back into the parabolic reflector, resulting in double loss of energy due to the reflectivity coefficients of the materials.

These and other features and objects of the present invention will be better understood by reference to the following detailed description in conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is a perspective view of an illumination unit according to the present invention with certain parts shown in exploded position and with a portion of the reflector shown broken away.

FIG. 2 is a cross-sectional view taken at 22 of FIG.

FIG. 3 is a cross-sectional view taken at 33 of FIG.

FIG. 4 is a cross-sectional view similar to FIG. 2 but in diagrammatic representation.

FIG. 5 is a diagrammatic representation for use in explaining the form of the principal reflective surfaces.

FIG. 6 is an enlarged diagrammatic view of the most rearward portion of the reflector for use in explaining a modified form of this portion of the reflector.

FIG. 7 is a diagrammatic cross-sectional view taken along the axis of the cylindrical illumination source.

FIG. 8 is a perspective view of a typical structural arrangement of an illumination system according to the present invention.

FIG. 9 is a perspective, diagrammatic view of photographic format illumination to aid in explaining a typical application of the present invention.

FIG. 10 is also a perspective, diagrammatic view of format illumination but arranged to provide a topological representation of ground irradiance.

FIG. 11 is a partial plan view of an illuminated ground format with the amplitude of ground irradiance indicated at plural points within the format.

FIGS. 12 through 16 are a series of diagrammatic plan views of the photographic format to aid in explaining the use of several illumination units to provide a composite format illumination in accordance with the present invention.

FIG. 17 is a diagrammatic plan view of the photographic format with a comparison by sectors of the theoretical ground irradiance with ground irradiance provided by the illumination system application described.

THE ILLUMINATION MODULE Referring now to the drawings, and more particularly to FIGS. 1 through 3 thereof, there is illustrated a preferred form of an illumination unit or module 10 in accordance with the present invention. In FIG. 1, to promote ease of understanding, certain parts of the illumination module 10 are illustrated in exploded position, and a portion of the reflector isshown broken away. The illumination module 10 comprises generally a cylindrical electronic flash tube 11 mounted within a trough-like reflector 12 which is arranged to provide an illumination beam of rectangular cross-sectional configuration. The flash tube 11 is located within, and is coaxial with, an optically transparent quartz tube 13 which extends through respective openings 14 in the

end plates

16 and 17 of the reflector. The ends of the quartz tube 13 are respectively received and supported within the bores 18 provided in the mounting blocks 19 of a pair of identical end mounting assemblies 20. The mounting blocks 19 are fabricated of electrical insulating material and are affixed to the

respective end plates

16 and 17 of the reflector by screws 21 or other suitable fastening means. The electrode terminals 15 at the ends of the flash tube 11 are each tightly received and supported by an electrically-conductive connecting clip 22. The connectingclips 22 are each secured in place by a compatible slotted recess 23 in the corresponding mounting block 19 and by an end fitting 24 which, in turn, is affixed to the mounting block 19 by the screws 21. Each of the end fittings 24 is fabricated of electrical insulating material and includes a cylindrical portion 25 providing an air passage to the bore of its associated mounting block 19 and the interior of the quartz tube 13. Each cylindrical portion 25 is capable of receiving an intake air manifold conduit. Thus, the quartz tube 13, the mounting blocks 19, and the end fittings 24 cooperate to form a cooling duct. Cooling air can be manifolded to enter either end of this duct and exhaust from the opposite end. To enhance heat dissipation, the connecting clips 22 are each provided with a plurality of radial fins 26 interposed in the cooling air flow path.

As illustrated in FIGS. 1 and 2, the reflector 12 is preferably provided with an outwardly-extending flange 31 along the perimeter of its illumination beam aperture. The purpose of this flange is to enhance the structural integrity of the reflector 12 and to provide one means for mounting the illumination module 10 in a frame.

It should be noted that the typical reflector 12 of the present invention illustrated in FIGS. 1 through 3 has a pair of interior, curvilinear, principal

reflective surfaces

27 and 28 which are symmetrical about a median plane 30 defined by geometric axis 29 of the cylindrical light source 11 and the center line of the reflector beam aperture. It is the function of these principal

reflective surfaces

27 and 28 to provide efficient distribution of emitted light weighted laterally (i. e., weighted in the directions perpendicular to the median plane 30). The

end plates

16 and 17 are also provided with interior reflective surfaces which, however, are not capable of distributing light in a weighted manner as precise as the

reflective surfaces

27 and 28. Hence, in a typical illumination system according to the present invention, one or more illumination modules will be arranged with the axes of their cylindrical light sources oriented parallel to the direction of flight to provide weighted distribution of light in the port and starboard directions, and one or more illumination modules 10 will be arranged with the axes of their cylindrical light sources oriented perpendicularly to the direction of flight to provide weighted distribution of light in the fore and aft directions. A typical illumination system arrangement is illustrated in FIG. 8 and will be described further on. At this point it will be helpful to gain a more specific understanding of the design of the reflective surfaces of the illumination module 10.

Referring now to FIG. 4, a cross-sectional view of the illumination module 10 taken in a plane perpendicular to the axis of the cylindrical light source 11 is presented in somewhat diagrammatic form. As previously indicated, the curved

reflective surfaces

27 and 28 function to provide efficient distribution of emitted light incident ray A nearer the aperture: of the reflector i2 is reflected at the half beam-width. angel of lS- w degrees with respect to the median plane 30 so as to fall on the opposite, outermost lateral edge of the desired illuminated format. The angle of convergence C and the corresponding equal angle of divergence D, are determined by the distance of the point P, from the geometric axis 29 of the illumination source 11 and the radius of the illumination source. Thus, if the point P is at a distance so as to provide an angle of divergence D equal to 17 degrees, the tangential ray B, from the more rearward side of the illumination source 11 will be reflected at an angle of 1-5: degrees with respect to the median plane 30 so as to fall in the opposite half of the illuminated format but in the central region of the format.

At the more forwardly located point P the slope of the reflective surface 27 again is such that the tangentially-emitted incident ray A closer to the reflector aperture is reflected at the half-beam-width angle of IS-r degrees relative to the median plane 30 so as to fall on weighted in the directions perpendicular to themedian plane in order to compensate for slant range and lens optical fall-off in these directions. This is accomplished in accordance with the recognition that the plasma discharge are of the light source 11 is a cylindrical source and not a line source. A high energy gaseous discharge flash tube may, for example, have a diameter of 12 millimeters. Thus, the light emitted from the cylindrical light source 11 is incident upon a given point on the parallel

reflective surfaces

27 and 28 in the form of a set of convergent rays having an included angle of convergence which is dependent upon the radius of the cylindrical light source 11 and the distance of the point of incidence from the geometric axis of the light source. The light reflected from the point of incidence is in the form of a set of divergent rays having an included angle of divergence which is equal to the angle of convergence of the incident light and a direction which is dependent upon the slope of the reflective surface at the point of incidence. In accordance with the present invention, the

reflective surfaces

27 and 28 are each formed to pass through a series of points each located at a distance from the geometric axis of the cylindrical light source and at a slope such that (l) the tangentially-emitted incident ray nearer the,desired aperture of the reflector at each of the points in the series is reflected at a predetermined half-beam-width angle with respect to the median plane 30 so as to fall upon the opposite, outermost lateral edge of the desired illumination format, and (2) the divergence angle of the set of reflected rays is gradually reduced at each of the points in the series so as to diminish from a predetermined maximum angle at the rearwardmost point on the reflective surface to ,a predetermined minimum angle at the forwardmost point on the reflective surface. a

In FIG. 4, two typical points P and P are illustrated on the reflective surface 27. Assuming for the purpose of explanation that the desired beam width of the illuminated format is 37 degrees, the slope of the reflective surface 27 at point P is such that tangentially-emitted the opposite, outermost edge of. the illuminated format. The point P however, is at a greater distance from the axis 29 of the illumination source than the point P such that the angles of convergence C and divergence D are smaller. Thus, if the angle of divergence D: from the point P is 6 degrees, the tangential ray B willbe reflected at an angle of l2-5 degrees with respect to the median plane 30 so as to fall in the'opposite, outer quarter of the illuminated format.

Thus, the points P and P typify the manner in-which the reflected light from the reflective surface 27 is weighted to provide a greater amount of light near the outer edge of the illuminationformat where the attenuation due to slant range and lens fall-off is greatest.

It has been found that by computing the requisite slope and distance from the illumination source axis at a sufficiently large yet finite number of points, a reflective surface can be generated for a particular weighted light distribution application in the form of substantially a continuous curve. Since the more points used in generating the surface the more accurate will .be the light distributed, the computations are preferably accomplished by a reiterative computer program. In order to better understand the configuration of the reflective surface and the basis for writing a computer program for a particular application, a description follows of the diagrammatic representation of FIG. 5.

In FIG. 5, a given point P, on the reflective surface 27 may be expressed in polar coordinates as being at a distance L from the geometric axis 29 of the illumination source ll at an angle X with respect to the desired median plane 30. Considering the illumination source 11 to have a radius R, the convergence angle C, of the incident light and the divergence angle D,, of the reflected light will each be approximately equal to 2 (arctan R /L The slope of the reflective surface at point P may be expressed in terms of the angle Y, formed by intersection of the median plane 30 with a line normal to the reflective surface at point P The reflected tangential ray A, intersects the median plane 30 at an angle J and the tangential ray 8,, intersects the median plane 30 at an angle K,,. The angle Y, is equal to J K,, 2X,,/4. In order to provide a continuous surface, the point P must be related to its preceding point P, In polar coordinates, the position of point P is advanced from the point P, 1 by a small angle AX and at a slightly greater distance AL. Thus,

L, R/arctan [(J, KQ/Z] The slope Y, is computed from the expression:

Y, (J, K, 2X,)/4

For all subsequent points P,,, AX increments are advanced, K, is selected, and L, and Y, are computed, 1,, being a constant half-beam-width angle at all points. The angle K, is gradually decreased at each point at a rate which will provide the desired illumination weighting. Thus, having selected K, at a particular point P,,, the following computations are necessary:

The principal parameters to be varied in generating a reflector surface for a given beam width and weighting factor are the distance L, to the first computed point and the change in the angle K, as the computation proceeds. K, can be varied, for example, as a linear function of AX, as an exponential function, or in other ways. Obviously, the greater the rate of increase of K,,, the greater the weighting factor of the reflective surface since more light will be directed toward the outer region of the illuminated format. In some instances, K, may be a negative angle at the more rearward points on the reflective surface. At such points, the ray B, will fall in the nearhalf of the format rather than in the opposite half. It should also be noted that while it would be preferable from the standpoint of precise format edge definition to prevent unwanted light spill outside of the desired format by continuing the

reflective surfaces

27 and 28 sufficiently forwardly that no direct, unreflected emitted light'leaves the reflector aperture at a greater angle relative to the median plane 30 than a half-beam-width angle, space limitations or other such factors in a given application may necessitate a more rearward termination of the

reflective surfaces

27 and 28 permitting a certain amount of direct light to spill outside of the desired format. The increase in efficiency due to precise distribution and weighting of the reflected light enabled by the present invention, however, normally renders such limited direct light spill-over rather negligible.

Referring now to FIG. 6, there is illustrated a modification in which a portion 41 of the reflector 12 behind the illumination source 11 is contoured to direct reflected light in this region around the illumination source 11 to avoid the blanking effect of the plasma arc. The reflective surface 41 is contoured to direct the sets of light rays from the several exemplary points M through M in a hugging" or tangential manner around the plasma until the point P, is reached at which the generation of the reflective surface 27 is begun in the manner described above. It should be noted at this juncture that other contours may be used for the reflective surface 41 if the blanking effect of the plasma is not considered significant. For example, if the point directly behind the illumination source 11 on the median plane 30 is at a distance such that the angle of convergence of the emitted light rays incident on this pointis equal to the full beam width angle, this may be used as the location of the beginning point P, for generating the reflective surface 27, or if less than a full beam width is used, the contour 41 may simply be a suitable contour which will provide a smooth curvilinear continuity from the reflector surface 28 to the beginning point P, of the reflector surface 27.

It should be understood that normally the reflective surface 28 will be generated as the minor image of the reflector surface 27. In unusual applications, however, the

reflective surfaces

27 and 28 may be asymmetrical or one of these surfaces may be generated in a manner other than as described herein.

Referring now to FIG. 7, there is provided a somewhat diagrammatic cross-sectiontaken along the geometric axis of the illumination source 11 for the purpose of explaining the design of the reflective surfaces of the

end plates

16 and 17 of the illumination unit 10. It has been found that the optimum arrangement of reflective surfaces for the end plates is to design these surfaces to look at the large smear or reflected light from the back surface of reflector 12 rather than plasma arc itself. Even though illumination from the back of the reflector 12 is in the form of reflection with intensity reduced by the reflectivity coefficient, it is a much larger area of light than that of the plasma arc itself. Thus, in FIG. 1, a pair of facets 42 and 43 are provided in the end plate 17 and oriented to direct light reflected from the back of the reflector 12 to the opposite, outer quarter of the illuminated format to provide a form of limited weighting of reflected light. Specifically, the facet 42 is designed to intercept light rays which leave the back surface of the reflector at a large acute angle relative to the normal to the back surface and reflect these light rays at an angle so as to fall inthe opposite, outer quarter of the format. For example, if the format beam width in a plane perpendicular to the axis of the light source is 74 degrees, the facet 42 may be oriented at an angle of 32 degrees so as to intercept rays which leave the back surface in the region 40 at an angle of 60 degrees with respect to the normal to the back surface and reflect theselight rays at a beam angle of 28 degrees so as to fall in the opposite, outer quarter of the format. Rays W and W are typical. The facet 43, for example, may be oriented at an angle of 17 degrees so as to intercept rays which leave the more distant portion of the region 40 at the smaller angle of 45 degrees with respect to the normal to the back surface and reflect these rays at an angle of 28 degrees so as to fall in the opposite, outer quarter of the format. Rays Z, and Z are typical. A pair of

facets

44 and 45 are similarly provided in the end plate 16.

THE ILLUMINATION SYSTEM Turning now from the consideration of the illumination module 10 to a consideration of a typical illumination system using more than one illumination module 10, reference is first made to FIG. 8 which illustrates an illumination system 46 which comprises a bank of six illumination modules mounted in a frame 47. It should be noted that two of the illumination modules (indicated by the reference numeral 10) have their axes perpendicular to the direction of flight while four of the illumination units (indicated by the reference numeral 10'') have their axes parallel to the direction of flight. The two illumination modules 10' provide weighted light distribution and format edge definition in the fore and aft directions while the four illumination units 10" provide weighted light distribution and format edge definition in the port and starboard directions.

The illumination system 46 illustrated in FIG. 8 includes a ram air intake 48 and manifold 49 for distributing ram cooling air through the several illumination units 10' and 10" via manifold conduits 50. The power supply and associated flash electrical circuitry are not a part of the present invention and, hence, are not shown.

To complete the understanding of the present invention, a description follows of a typical application of an illumination system in accordance with the invention.

Referring to FIG. 9, there is provided a diagrammatic perspective illustration of the photographic geometry of a typical illumination system application. By way of example, it may be assumed that the requirement is to illuminate a photographic format 74 degrees wide in the lateral direction and 74 degrees wide in the longitudinal direction from an aircraft 60 at an altitude of 500 feet with the camera optical axis at an angle of 20 degrees aft of the aircraft nadir N. Since the camera axis is tilted aft, the square illumination beam will image as a trapezoid 63 on the ground as illustrated. The angle a is the lateral half-beam-width angle which in this example is equal to 37 degrees. The angle 0 is the angle from the nadir N to any point P, on the ground format F. The angle (1; is the angle from the camera axis 0 to any point P, on the ground format. 1

Assuming that the fall-off attenuation for the lens to be used is a cosgb function, the required ground irradiance in joules per square meter is given by the expressron:

where:

E ground irradiance at the optical axis, and

Sec compensation for the cos lens fall-off characteristic. FIG. is a perspective diagrammatic illustration of a topological plot of ground irradiance E, throughout the ground format.

The beam intensity distribution necessary to produce the required ground irradiance distribution must be determined. Ground irradiance is related to source intensity l by:

r slant range at any point P, on the ground format, and

H the altitude of the aircraft. Compensation must be made for the cos fl slant range attenuation term, and the theoretical intensity distribution in joules per steradian becomes:

I 1,, sec 0 sec" where:

I the value of radiant intensity at the nadir.

FIG. 11 is a representation of the computed theoretical radiant intensity I at plurality of representative points in the ground format F.

Referring now to FIGS. 12 through 16, a series of diagrammatic representations of the ground format F are provided which illustrate the generation of the requisite beam intensity distribution for the ground format F by a composite of beams from an array of six' illumination modulesf In FIG. 12, the aft portion of the: ground format F is illuminated by two illumination modules each arranged with its lamp axis parallel to the line of flight and inclined at an angle of 49.6 degrees aft of the nadir and having a beam width of 74 degrees in a plane perpendicular to the direction of flight beam width of l4.8 degrees in a plane parallel to the direction of flight. The rleative intensity weighting factor of eachmodule in the outer lateral 13 degrees of the beam as compared to the central portion of the beam is 2 to l. The two illumination beams are congruent on the formatF, producing the composite intensity distribution as shown in FIG. 12.

The intensity distribution pattern shown in FIG. 13 is produced by the beams of two illumination modules inclined 12.6 degrees aft of the nadir with their lamp axes parallel to the direction of flight. The beam width from each module in a plane perpendicular to the line of flight is 74 degrees, and the beam width in a plane parallel to the line of flight is 59.2 degrees. In this case, the weighting factor of each module for the outer 13 degrees as compared with the central portion of the beam is 0.50 to 0.25. It should be noted that while the weighting ratio of the modules providing the illumination pattern of FIG. 13 is the same as for the modules providing the illumination pattern of FIG. 12 (i.e., twice as much light intensity in the outer 13 degrees of the format as in the central portion), the area of the beam in FIG. l3'is much larger with the result that the overall density of illumination in the FIG. 13 pattern is less than that of the FIG. 12 pattern.

The illumination pattern shown in FIG. 14 is produced by a single illumination module arranged with its lamp axis parallel to the line of flight and inclined 38.5 degrees aft of the nadir. The dimensions of the beam from this module are 74 degrees in the plane perpendicular to the line of flight and 37 degrees in the plane of the line of flight. The reflective surfaces in this module are contoured to provide a weighting factor for the outer 25 degrees on each side of the pattern compared with the central portion of the pattern of 1.35 to 0.45, as indicated.

The sixth module is arrangedwith its lamp axis perpendicular to the direction of flight. The center line of the beam is directed 20 degrees aft of the nadir (coincident with the camera optical axis), and the reflector is designed to provide a 74 degree by a 74 degree beam to cover the entire area of the format as illustrated in FIG. 15. In this instance, the reflector is contoured to weight the fore and aft l4.8 degree sectors of the pattern as compared with the central portion of the pattern by a factor of 1 to 0.25.

FIG. 16 provides a composite of the illumination patterns shown in FIGS. 12 through 15 with an average intensity summation for each segment of the format F. In

FIG. 17, the approximate average intensity provided in each segment is compared with the approximate theoretical average intensity (in blocks) for each segment from the intensity distribution map of FIG. 11. As seen, the illumination system provides an intensity distribution very comparable to the theoretical intensity distribution for the particular application.

From the foregoing description, it is apparent that the present invention provides a versatile optical illumination system which has the important capability for producing an efficient, well-defined illumination intensity distribution which will compensate for the attenuating effects of slant range and lens fall-off.

The specific examples herein shown and described are illustrated only. Various changes in structure will, no doubt, occur to those skilled in the art, and these changes are to be understood as forming a part of this invention insofar as they fall within the spirit and scope of the appended claims.

What is claimed is:

1. An aircraft mounted ground illumination system for an optical lens system comprising:

a plurality of illumination modules, each comprising a cylindrical light source and a trough-like reflector having a rectangular beam aperture and a pair of curved reflective surfaces parallel with the gemoetric axis of said cylindrical light source and formed to provide reflected light distribution weighted in a plane perpendicular to the geometric axis of said light source, at least a first one of said illumination modules being arranged with its axis parallel to a given direction so as to provide light distribution weighted in a plane perpendicular to said given direction, and at least a second one of said illumination modules being arranged with its axis perpendicular to said given direction so as to provide light distribution weighted in a plane parallel to said given direction, at least said first and second illumination modules illuminating in common at least a predetermined portion of a desired ground-imaged format additively in accordance with the expression where l is radiant light intensity, I is the value of radiant intensity at the nadir, 0 is the slant range angle to said portion as measured from the nadir, (b is the optical lens fall-off angle to said portion as measured from the optical axis of said desired format, and n is an exponent indicative of the off-axis optical characteristic of the optical lens used.

2. An optical illumination system as defined in claim 1 wherein each of said illumination modules has at least one curved reflective surface which is parallel to the axis of said cylindrical light source and which extends through a series of points, said reflective surface at each of said points being spaced from the geometric axis of said cylindrical light source and having a slope one another about a median plane defined by the geometric axis of said cylindrical light source and the center line of the illumination beam aperture of said reflector, each of said reflective surfaces extending through a series of points, the reflective surface at each of said points being spaced from the geometric axis of said cylindrical light source and having a slope reflecting the tangentially-emitted incident ray nearer the aperture of the reflector at a predetermined half-beam-width angle relative to said median plane for incidence 'upon the opposite outermost edge of the illumination format, the spacing of said points from the geometric axis of said cylindrical light source being increased at each successive one of said points to diminish the divergence angle of the reflected rays at each successive one of said points in said series from a predetermined maximum angle at the first point in said series to a predetermined minimum angle at the last point in said series.

4. An optical illumination system as defined in claim 1 further comprising:

an intake for cooling air; manifold means for distributing cooling air from said intake to said illumination modules, each of said illumination modules having an optically transparent quartz tube within which said cylindrical illumination source is coaxially disposed; means for conducting cooling air from said manifold means to one end of said quartz tube; and means for exhausting cooling air from the opposite end of said quartz tube. 5. An optical illumination system as defined in claim 4 wherein each of said illumination modules includes electrical connection clips for the-electrodes of said cylindrical light source, said connection clips having a plurality of radial fins interposed in the cooling air flow through said quartz tube.

6. An optical illumination unit comprising: a cylindrical light source, and a trough-like reflector having a rectangular beam aperture and having at least one curved reflective surface which is parallel to the axis of said cylindrical light source and which extends through a series of points; g the distance L, of said reflective surface from the geometric axis of said cylindrical light source at the first (rearwardmost) point in said series being defined by the expression wherein R is the radius of said cylindrical light source, J, is the predetermined half-beam-width angle, and K, is a selected angle which is less than a half-beam-width angle;

the slope Y, of said reflective surface at said first point in said series being defined by the expression wherein X, is the polar coordinate angle of said first point P, in said series as related to the geometric axis of said cylinder light source as measured from a center plane passed through the geometric axis of the light source and the center line of the illumination beam aperture of said reflector;

the slope Y, of said reflective surface at every other point P, in said series being defined by the espression wherein J, is constant equal to the half-beam-width angle 1,, K,, is an angle selected to have the characteristic K,, K,, l K,, and X is the polar coordinate angle of the point P, with X having the characteristic X,

ric axis of said cylindrical light source and formed to provide reflected light distribution weighted in a plane perpendicular to the geometric axis of said light source, at least a first one of said illumination modules being arranged with its axis parallel to a given direction so as to provide light distribution weighted in a plane perpendicular to said given direction, and at least a second one of said illumination modules being'arranged with its axis perpendicular to said given direction so as to provide light distribution weighted in a plane parallel to said given direction, at least said first and second illumination modules illuminating in common at least a predetermined portion of a desired ground-imaged format additively in accordance with the expression I E H /Cos 6 where I is radiant light intensity, E is ground irradiance compensated for the off-axis optical characteristic of the optical lens used, H is the aircraft altitude at which the optical lens is to be used, and 0 is the slant range angle to said portion as measured from the nadir.

Claims

1. An aircraft mounted ground illumination system for an optical lens system comprising: a plurality of illumination modules, each comprising a cylindrical light source and a trough-like reflector having a rectangular beam aperture and a pair of curved reflective surfaces parallel with the geometric axis of said cylindrical light source and formed to provide reflected light distribution weighted in a plane perpendicular to the geometric axis of said light source, at least a first one of said illumination modules being arranged with its axis parallel to a given direction so as to provide light distribution weighted in a plane perpendicular to said given direction, and at least a second one of said illumination modules being arranged with its axis perpendicular to said given direction so as to provide light distribution weighted in a plane parallel to said given direction, at least said first and second illumination modules illuminating in common at least a predetermined portion of a desired ground-imaged format additively in accordance with the expression I Io sec2 theta secn phi where I is radiant light intensity, Io is the value of radiant intensity at the nadir, theta is the slant range angle to said portion as measured from the nadir, phi is the optical lens fall-off angle to said portion as measured from the optical axis of said desired format, and n is an exponent indicative of the off-axis optical characteristic of the optical lens used.

2. An optical illumination system as defined in claim 1 wherein each of said illumination modules has at least one curved reflective surface which is parallel to the axis of said cylindrical light source and which extends through a series of points, said reflective surface at each of said points being spaced from the geometric axis of said cylindrical light source and having a slope reflecting the tangentially-emitted incident ray nearer the aperture of the reflector at a predetermined half-beam-width angle relative to a center plane defined by the geometric axis of the light source and the center line of illumInation beam aperture of said reflector for incidence upon the opposite outermost edge of the illumination format, the spacing of said points from the geometric axis of said cylindrical light source being increased at each successive one of said points to diminish the divergence angle of the reflected rays at each successive one of said points in said series from a predetermined maximum angle at the first point in said series to a predetermined minimum angle at the last point in said series.

3. An optical illumination system as defined in claim 5 wherein each of said illumination modules has a pair of curved reflective surface regions symmetrical with one another about a median plane defined by the geometric axis of said cylindrical light source and the center line of the illumination beam aperture of said reflector, each of said reflective surfaces extending through a series of points, the reflective surface at each of said points being spaced from the geometric axis of said cylindrical light source and having a slope reflecting the tangentially-emitted incident ray nearer the aperture of the reflector at a predetermined half-beam-width angle relative to said median plane for incidence upon the opposite outermost edge of the illumination format, the spacing of said points from the geometric axis of said cylindrical light source being increased at each successive one of said points to diminish the divergence angle of the reflected rays at each successive one of said points in said series from a predetermined maximum angle at the first point in said series to a predetermined minimum angle at the last point in said series.

4. An optical illumination system as defined in claim 1 further comprising: an intake for cooling air; manifold means for distributing cooling air from said intake to said illumination modules, each of said illumination modules having an optically transparent quartz tube within which said cylindrical illumination source is coaxially disposed; means for conducting cooling air from said manifold means to one end of said quartz tube; and means for exhausting cooling air from the opposite end of said quartz tube.

5. An optical illumination system as defined in claim 4 wherein each of said illumination modules includes electrical connection clips for the electrodes of said cylindrical light source, said connection clips having a plurality of radial fins interposed in the cooling air flow through said quartz tube.

6. An optical illumination unit comprising: a cylindrical light source, and a trough-like reflector having a rectangular beam aperture and having at least one curved reflective surface which is parallel to the axis of said cylindrical light source and which extends through a series of points; the distance Ls of said reflective surface from the geometric axis of said cylindrical light source at the first (rearwardmost) point in said series being defined by the expression Ls R/arctan ((Js - Ks)/2) wherein R is the radius of said cylindrical light source, Js is the predetermined half-beam-width angle, and Ks is a selected angle which is less than a half-beam-width angle; the slope Ys of said reflective surface at said first point in said series being defined by the expression Ys (Js + Ks +2Xs)/4 wherein Xs is the polar coordinate angle of said first point Ps in said series as related to the geometric axis of said cylindrical light source and as measured from a center plane passed through the geometric axis of the light source and the center line of the illumination beam aperture of said reflector; the slope Yn of said reflective surface at every other point Pn in said series being defined by the expression Yn (Jn + Kn + 2Xn)/4 wherein Jn iS constant equal to the half-beam-width angle Js, Kn is an angle selected to have the characteristic Kn>Kn 1 >Ks, and Xn is the polar coordinate angle of the point Pn with Xn having the characteristic Xn Delta X + Xn 1; the distance Ln of said reflective surface from the geometric axis of said cylindrical light source at Pn being defined by the expression Ln Ln 1 (1 + sin Delta X tan (Xn 1 + ( Delta X/2) - Yn 1)).

7. An aircraft mounted ground illumination system for an optical lens system comprising: a plurality of illumination modules, each comprising a cylindrical light source and a trough-like reflector having a rectangular beam aperture and a pair of curved reflective surfaces parallel with the geometric axis of said cylindrical light source and formed to provide reflected light distribution weighted in a plane perpendicular to the geometric axis of said light source, at least a first one of said illumination modules being arranged with its axis parallel to a given direction so as to provide light distribution weighted in a plane perpendicular to said given direction, and at least a second one of said illumination modules being arranged with its axis perpendicular to said given direction so as to provide light distribution weighted in a plane parallel to said given direction, at least said first and second illumination modules illuminating in common at least a predetermined portion of a desired ground-imaged format additively in accordance with the expression I EgH2/Cos2 theta where I is radiant light intensity, Eg is ground irradiance compensated for the off-axis optical characteristic of the optical lens used, H is the aircraft altitude at which the optical lens is to be used, and theta is the slant range angle to said portion as measured from the nadir.